The present invention relates to a method and to a sensor for determining the distance of sound generating targets with respect to the sensor by means of acoustic signals subjected to a Fourier transformation.
DE-OS (German Unexamined Published Patent Application) 3,936,359 discloses the use of a sensor arrangement composed of a plurality of sensors to determine the direction and distance of sound generating targets, with acoustic sensors being employed to determine the target direction. A seismic sensor is additionally employed to determine the target distance. A line characteristic of the target in the air and ground sound spectra is measured and the Doppler shift between these lines as well as the propagation speed of the corresponding waves are used to calculate the radial target velocity and from it, under consideration of the bearing angle, the target distance. Aside from the fact that a number of sensors are required to determine the target distance, the propagation speed of sound waves in the ground relative to the propagation speed of sound waves in the air fluctuates greatly depending on the type of ground involved so that this propagation speed must be determined which requires the formation of a cross spectrum of the signals received from two sensors.